Metallic microneedles

ABSTRACT

Methods for fabricating metallic microneedles are disclosed. One method comprises providing a mold pillar; forming an apertured electrically-conductive layer over the mold pillar; and depositing a metal layer over the electrically-conductive layer to provide an apertured microneedle. Another method comprises providing a mold pillar; depositing a first metal layer over the mold pillar to provide a first microneedle; removing the first microneedle from the mold pillar; and depositing a second metal layer over the mold pillar to provide a second microneedle.

RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/595,891 which is, in turn, a continuation of U.S. application Ser.No. 14/965,536 filed 10 Dec. 2015 (now U.S. Pat. No. 9,675,790) whichis, in turn, a continuation of PCT application No. PCT/CA2014/050552having an international filing date of 12 Jun. 2014. PCT application No.PCT/CA2014/050552 in turn claims the benefit of the priority of U.S.application No. 61/834,482 filed 13 Jun. 2013. All of U.S. applicationSer. No. 15/595,891, U.S. application Ser. No. 14/965,536, PCTapplication No. PCT/CA2014/050552 and U.S. application No. 61/834,482are hereby incorporated herein by reference.

TECHNICAL FIELD

This invention relates to methods for fabricating mechanicalmicrostructures. In particular, this invention relates to methods forfabricating metallic microneedles.

BACKGROUND

Various methods for fabricating microneedles are known. Examples ofknown techniques include those described in the following disclosures:

-   D. V. McAllister et al., Microfabricated needles for transdermal    delivery of macromolecules and nanoparticles: Fabrication methods    and transport studies, (2003), Proc. Nat. Acad. Sci. USA, Vol.    100(24), pp. 13755-13760.-   B. Stoeber, D. Liepmann, Arrays of Hollow out-of-Plane Microneedles    for Drug Delivery, (2005), J. Microelectromech. Syst., Vol. 14, no.    3, pp. 472-479.-   I. Mansoor et al. Hollow Out-of-Plane Polymer Microneedles Made by    Solvent Casting for Transdermal Drug Delivery, (2012), J.    Microelectromech. Syst., Vol. 21, pp. 44-52.-   S. P. Davis et al., Hollow metal microneedles for insulin delivery    to diabetic rats, (2005), IEEE Trans. Biomed. Eng., Vol. 52, pp.    909-915.-   U.S. Pat. No. 7,627,938 (Kim et al.).

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with methods and apparatus which are meant tobe exemplary and illustrative, not limiting in scope.

One aspect of this invention provides a method for fabricating anapertured microneedle. The method comprises providing a mold pillar;forming an apertured electrically-conductive layer over the mold pillar;and depositing a metal layer over the apertured electrically-conductivelayer to provide an apertured microneedle.

In some embodiments, the mold pillar extends away from a surface of asubstrate. The mold pillar may extend away from the surface of thesubstrate in a direction generally normal to the surface of thesubstrate. The mold pillar may comprise a photoresist and providing themold pillar may comprise exposing the photoresist to actinic radiationthrough a mask. The mask may comprise a circular-shaped region which istransparent to actinic radiation. The mold pillar may comprise acone-shaped mold pillar with a base and a tip. Providing the mold pillarmay comprise using an etching process to sharpen the tip of the moldpillar. In some embodiments the mold pillar comprises a protective layerfor protecting the mold pillar from subsequent processes and enablinguse of the mold pillar for fabricating a plurality of microneedles. Themethod may comprise forming the protective layer using a solvent-castingprocess.

In some embodiments forming the apertured electrically-conductive layerover the mold pillar comprises using a solvent-casting process.Solvent-casting the electrically-conductive layer may comprise adding apolymer and conductive particles to a solvent. The polymer may comprisepoly(methyl methacrylate) (PMMA) and the conductive particles maycomprise carbon black particles. The method may comprise adding asurfactant to the solvent. The apertured electrically-conductive layermay comprise a uniform distribution of the conductive particles withinthe polymer. Forming the apertured electrically-conductive layer overthe mold pillar may comprise coating the mold pillar with theelectrically-conductive layer and then removing a portion of theelectrically-conductive layer to form an aperture. The method maycomprise removing the portion of the electrically-conductive layer bydry etching. The method may comprise removing the portion of theelectrically-conductive layer by photolithography. The method maycomprise removing the portion of the electrically-conductive layer bymechanical grinding. The method may comprise removing the portion of theelectrically-conductive layer by localized heating. The method mayfurther comprise forming the apertured electrically-conductive layer byapplying a coating to a region of the mold pillar and solvent-castingthe electrically-conductive layer onto the mold pillar using a solventthat is repelled by the coating so that the electrically-conductivelayer is created with an aperture located at the coated region. Thecoating may comprise a polar coating and the solvent may comprise anon-polar solvent, or the coating is a non-polar coating and the solventis a polar solvent. The method may further comprise forming theapertured electrically-conductive layer by orienting the mold pillar sothat a first region of the mold pillar is vertically higher than asecond region of the mold pillar and solvent-casting theelectrically-conductive layer onto the mold pillar so that the force ofgravity causes the electrically-conductive layer to form with anaperture at the first region.

In some embodiments, depositing the metal layer over the aperturedelectrically-conductive layer comprises electroplating the metal layeronto the apertured electrically-conductive layer and using the aperturedelectrically-conductive layer as an electrode in the electroplatingprocess. The metal layer may comprise a first sub-layer of metaladjacent the electrically-conductive layer and second sub-layer of metaladjacent the first layer of metal. The first sub-layer of metal maycomprise a structural metal and the second sub-layer of metal maycomprise a biocompatible metal; or the first metal sub-layer maycomprise a biocompatible metal and the second metal sub-layer maycomprise a structural metal.

In some embodiments, the method may comprise removing the microneedlefrom the mold pillar. Removing the microneedle from the mold pillar maycomprise at least partially dissolving the aperturedelectrically-conductive layer. Removing the microneedle from the moldpillar may comprise at least partially dissolving a sacrificial layerformed over the mold pillar. The sacrificial layer may be formed betweenthe mold pillar and the apertured electrically conductive layer.Removing the microneedle from the mold pillar may leave the mold pillarsubstantially intact. The method may further comprise re-using the moldpillar to fabricate a second microneedle. Re-using the mold pillar tofabricate the second microneedle may comprise forming a second aperturedelectrically-conductive layer over the mold pillar and depositing asecond metal layer over the second apertured electrically-conductivelayer to provide the second microneedle. Re-using the mold pillar tofabricate the second microneedle may comprise depositing a second metallayer over the apertured electrically-conductive layer to provide thesecond microneedle.

In some embodiments the method further comprises applying a coating tothe microneedle. The coating may comprise a biocompatible coating. Thecoating may comprise an electrically-insulating coating. The method maycomprise removing the microneedle from the mold pillar and applying thecoating to an interior surface of the microneedle, the interior surfaceof the microneedle masked by the mold pillar prior to removal of themicroneedle from the mold pillar. The method may comprise forming asacrificial layer over the mold pillar. Depositing the first metal layerover the mold pillar comprises sputtering the first metal layer over thesacrificial layer. Removing the first microneedle from the mold pillarmay comprise at least partially dissolving the sacrificial layer. Thecoating may comprise metal. Applying the metal coating to the interiorsurface of the microneedle may comprise electroplating the metal coatingover the interior surface of the microneedle and using the microneedleas an electrode in the electroplating process. The coating may comprisea biocompatible coating.

Another aspect of the invention provides a method for fabricating afirst microneedle and a second microneedle. The method comprises:providing a mold pillar; depositing a first metal layer over the moldpillar to provide a first microneedle; removing the first microneedlefrom the mold pillar; and depositing a second metal layer over the moldpillar to provide a second microneedle.

In some embodiments, the mold pillar extends away from a surface of asubstrate. The mold pillar may extend away from the surface of thesubstrate in a direction generally normal to the surface of thesubstrate. The mold pillar may comprise a photoresist and providing themold pillar may comprise exposing the photoresist to actinic radiationthrough a mask. The mask may comprise a circular-shaped region which istransparent to actinic radiation. The mold pillar may comprise acone-shaped mold pillar with a base and a tip. Providing the mold pillarmay comprise using an etching process to sharpen the tip of the moldpillar. In some embodiments the mold pillar comprises a protective layerfor protecting the mold pillar from subsequent processes and enablinguse of the mold pillar for fabricating a plurality of microneedles. Themethod may comprise forming the protective layer using a solvent-castingprocess.

In some embodiments, depositing a first metal layer over the mold pillarto provide the first microneedle comprises forming anelectrically-conductive layer over the mold pillar; and depositing thefirst metal layer over the electrically-conductive layer. Forming theelectrically-conductive layer over the mold pillar may comprise using asolvent-casting process. Solvent-casting the electrically-conductivelayer may comprise adding a polymer and conductive particles to asolvent. The polymer may comprise poly(methyl methacrylate) (PMMA) andthe conductive particles may comprise carbon black particles. The methodmay comprise adding a surfactant to the solvent. Theelectrically-conductive layer may comprise a uniform distribution of theconductive particles within the polymer. The electrically-conductivelayer may comprise an apertured electrically-conductive layer. Themethod may further comprise forming the aperturedelectrically-conductive layer by coating the mold pillar with theelectrically-conductive layer and then removing a portion of theelectrically-conductive layer to form an aperture. The method maycomprise removing the portion of the electrically-conductive layer bydry etching. The method may comprise removing the portion of theelectrically-conductive layer by photolithography. The method maycomprise removing the portion of the electrically-conductive layer bymechanical grinding. The method may comprise removing the portion of theelectrically-conductive layer by localized heating. Forming theelectrically-conductive layer over the mold pillar may comprise applyinga coating to a region of the mold pillar and solvent-casting theelectrically-conductive layer onto the mold pillar using a solvent thatis repelled by the coating so that the electrically-conductive layer iscreated with an aperture located at the coated region. The coating maycomprise a polar coating and the solvent may comprise a non-polarsolvent, or the coating may comprise a non-polar coating and the solventmay comprise a polar solvent. Forming the aperturedelectrically-conductive layer over the mold pillar may compriseorienting the mold pillar so that a first region of the mold pillar isvertically higher than a second region of the mold pillar andsolvent-casting the electrically-conductive layer onto the mold pillarso that the force of gravity causes the electrically-conductive layer toform with an aperture at the first region.

In some embodiments, depositing the first metal layer over theelectrically conductive layer comprises using theelectrically-conductive layer as an electrode and electroplating thefirst metal layer onto the electrically-conductive layer. The firstmetal layer may comprise a first metal sub-layer applied over theelectrically-conductive layer and a second metal sub-layer applied overthe first metal sub-layer. The first metal sub-layer may comprise astructural metal and the second metal sub-layer may comprise abiocompatible metal.

In some embodiments, removing the first microneedle from the mold pillarcomprises at least partially dissolving the electrically-conductivelayer. Removing the first microneedle from the mold pillar may compriseat least partially dissolving a sacrificial layer formed over the moldpillar. The method may comprise forming a sacrificial layer between themold pillar and the electrically-conductive layer and removing the firstmicroneedle from the mold pillar may comprise at least partiallydissolving the sacrificial layer. Removing the first microneedle fromthe mold pillar may leave the mold pillar substantially intact. Themethod may further comprise applying a coating to the first microneedle.The coating may comprise a biocompatible coating. The coating maycomprise an electrically-insulating coating. The method may comprise,after removing the first microneedle from the mold pillar, applying acoating to an interior surface of the first microneedle, the interiorsurface of the first microneedle masked by the mold pillar prior toremoval of the first microneedle from the mold pillar. The coating maycomprise metal. Applying the metal coating to the interior surface ofthe first microneedle may comprise electroplating the metal coating overthe interior surface of the first microneedle using the firstmicroneedle as an electrode in the electroplating process. The coatingmay comprise a biocompatible coating. Depositing the second metal layerover the mold pillar to provide the second microneedle may comprisedepositing the second metal layer over the electrically-conductive layerto provide the second microneedle.

Depositing the second metal layer over the mold pillar to provide thesecond microneedle may comprise forming a second electrically-conductivelayer over the mold pillar and depositing the second metal layer overthe second electrically-conductive layer to provide the secondmicroneedle.

Another aspect of the invention provides a method for fabricating amicroneedle. The method comprises providing a mold pillar; forming anelectrically-conductive polymer layer over the mold pillar; anddepositing a metal layer over the electrically-conductive polymer layerto provide a microneedle.

In some embodiments, the mold pillar extends away from a surface of asubstrate. The mold pillar may extend away from the surface of thesubstrate in a direction generally normal to the surface of thesubstrate. The mold pillar may comprise a photoresist and providing themold pillar may comprise exposing the photoresist to actinic radiationthrough a mask. The mask may comprise a circular-shaped region which istransparent to actinic radiation. The mold pillar may comprise acone-shaped mold pillar with a base and a tip. Providing the mold pillarmay comprise using an etching process to sharpen the tip of the moldpillar. In some embodiments the mold pillar comprises a protective layerfor protecting the mold pillar from subsequent processes and enablinguse of the mold pillar for fabricating a plurality of microneedles. Themethod may comprise forming the protective layer using a solvent-castingprocess.

In some embodiments forming the electrically-conductive polymer layerover the mold pillar comprises using a solvent-casting process.Solvent-casting the electrically-conductive polymer layer may compriseadding a polymer and conductive particles to a solvent. The polymer maycomprise poly(methyl methacrylate) (PMMA) and the conductive particlesmay comprise carbon black particles. The method may comprise adding asurfactant to the solvent. The electrically-conductive polymer layer maycomprise a uniform distribution of the conductive particles within thepolymer. The electrically-conductive polymer layer may comprise anapertured electrically-conductive polymer layer. The method may compriseforming the apertured electrically-conductive polymer layer by coatingthe mold pillar with the electrically-conductive polymer layer and thenremoving a portion of the electrically-conductive polymer layer to forman aperture. The method may comprise removing the portion of theelectrically-conductive polymer layer by dry etching. The method maycomprise removing the portion of the electrically-conductive polymerlayer by photolithography. The method may comprise removing the portionof the electrically-conductive polymer layer by mechanical grinding. Themethod may comprise removing the portion of the electrically-conductivepolymer layer by localized heating. The method may comprise forming theapertured electrically-conductive polymer layer by applying a coating toa region of the mold pillar and solvent-casting theelectrically-conductive polymer layer onto the mold pillar using asolvent that is repelled by the coating so that theelectrically-conductive polymer layer is created with an aperturelocated at the coated region. The coating may comprise a polar coatingand the solvent may comprise a non-polar solvent, or the coating maycomprise a non-polar coating and the solvent may comprise a polarsolvent. The method may further comprise forming the aperturedelectrically-conductive polymer layer over the mold pillar by orientingthe mold pillar so that a first region of the mold pillar is verticallyhigher than a second region of the mold pillar and solvent-casting theelectrically-conductive polymer layer onto the mold pillar so that theforce of gravity causes the electrically-conductive polymer layer toform with an aperture at the first region.

In some embodiments, depositing the metal layer over theelectrically-conductive layer comprises electroplating the metal layeronto the electrically-conductive polymer layer and using theelectrically-conductive polymer layer as an electrode in theelectroplating process. Depositing the metal layer over theelectrically-conductive polymer layer may comprise sputtering the metallayer onto the electrically-conductive polymer layer. The metal layermay comprise a first sub-layer of metal adjacent theelectrically-conductive polymer layer and second sub-layer of metaladjacent the first layer of metal. The first sub-layer of metal maycomprise a structural metal and the second sub-layer of metal maycomprise a biocompatible metal; or the first metal sub-layer maycomprise a biocompatible metal and the second metal sub-layer maycomprise a structural metal.

In some embodiments, the method comprises removing the microneedle fromthe mold pillar. Removing the microneedle from the mold pillar maycomprise at least partially dissolving the electrically-conductivepolymer layer. Removing the microneedle from the mold pillar maycomprise at least partially dissolving a sacrificial layer formed overthe mold pillar. The sacrificial layer may be formed between the moldpillar and the electrically-conductive polymer layer. Removing themicroneedle from the mold pillar may leave the mold pillar substantiallyintact. The method may further comprise re-using the mold pillar tofabricate a second microneedle. Re-using the mold pillar to fabricatethe second microneedle may comprise forming a secondelectrically-conductive polymer layer over the mold pillar anddepositing a second metal layer over the second electrically-conductivepolymer layer to provide the second microneedle. Re-using the moldpillar to fabricate the second microneedle may comprise depositing asecond metal layer over the electrically-conductive polymer layer toprovide the second microneedle.

In some embodiments, the method further comprises applying a coating tothe microneedle. The coating may comprise a biocompatible coating. Thecoating may comprise an electrically-insulating coating. The method mayfurther comprise removing the microneedle from the mold pillar; andapplying the coating to an interior surface of the microneedle, theinterior surface of the microneedle masked by the mold pillar prior toremoval of the microneedle from the mold pillar. The coating maycomprise metal. Applying the metal coating to the interior surface ofthe microneedle may comprise electroplating the metal coating over theinterior surface of the microneedle and using the microneedle as anelectrode in the electroplating process. The coating may comprise abiocompatible coating.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following detailed descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be considered illustrative rather than restrictive.

FIGS. 1A-1G (collectively, FIG. 1) are cross-sectional views whichdepict a method for fabricating metallic microneedle(s) according toexample embodiment(s).

FIG. 2 is a schematic diagram showing a method for fabricating ametallic microneedle according to an example embodiment.

FIG. 3 is a schematic diagram showing a method for fabricating ametallic microneedle according to an example embodiment.

FIG. 4A is a schematic plan view of an asymmetrically shaped mold pillaraccording to a particular embodiment. FIG. 4B is a schematic plan viewof an asymmetrically shaped aperture formed in an electricallyconductive layer according to a particular embodiment.

FIG. 5 is a schematic diagram showing a method for fabricating ametallic microneedle according to an example embodiment.

DESCRIPTION

Throughout the following description specific details are set forth inorder to provide a more thorough understanding to persons skilled in theart. However, well known elements may not have been shown or describedin detail to avoid unnecessarily obscuring the disclosure. Accordingly,the description and drawings are to be regarded in an illustrative,rather than a restrictive, sense.

One embodiment of the invention provides a method for manufacturing ametallic microneedle. The method may comprise: providing a mold pillar;forming an electrically-conductive layer over the mold pillar;depositing a metal layer over the electrically-conductive layer toprovide a microneedle; and removing the microneedle from the moldpillar. The electrically-conductive layer may be apertured prior todeposition of the electrically conductive layer to form an aperturedmetal layer and a correspondingly apertured microneedle. The mold pillarmay be reused to fabricate additional metallic microneedles.

Fabricating or Otherwise Providing a Mold Pillar

A mold pillar may be fabricated by any suitable method includingmicromachining (e.g. silicon micromachining), embossing (e.g. hotembossing), lithography (e.g. soft lithography and optical lithography),3D printing and/or the like. The mold pillar may comprise any suitablematerial. In some embodiments, a previously fabricated microneedle maybe used as the mold pillar.

The mold pillar may have any suitable shape and may comprise a column,post, cone, wall, etc. The mold pillar may be fabricated to extend awayfrom (or may otherwise extend away from) a substrate. The substrate maycomprise any suitable material including silicon, glass, Pyrex®, quartz,polymer, metal, ceramic, and any combination thereof. The mold pillarmay extend from the surface of the substrate in any direction(s)including, where the substrate is generally planar, in out-of-planedirections (e.g. in direction(s) which have at least a component that isnormal to the generally planar surface of the substrate). Inembodiments, where the substrate is non-planar, the mold pillar mayextend in direction(s) which have at least a component that is normal tothe surface of the substrate at the location of the mold pillar. Anarray comprising a plurality of mold pillars may be fabricated orotherwise provided on the surface of the substrate. As will become clearfrom the description that follows, the spacing and arrangement of thearray of mold pillars may define the spacing and arrangement of an arrayof microneedles fabricated using the array of mold pillars.

FIGS. 1A and 1B show a method for fabricating an array of mold pillars110 according to an example embodiment. A photoresist 102 may be appliedto a first surface 104A of a substrate 104 and a mask 106 may be appliedto the opposing surface 104B of substrate 104. The masked surface 104Bof substrate 104 may be exposed to actinic radiation 108. After theexposure to actinic radiation 108, photoresist 102 may be submerged in adeveloper bath, thereby dissolving some of photoresist 102 and leavingbehind mold pillars 110 (FIG. 1B). The illustrated embodiment of FIGS.1A and 1B involves using a negative photoresist 102 (where exposedphotoresist is maintained after exposure to provide mold pillars 110).In some embodiments, a positive photoresist may be used (such thatexposed photoresist is dissolved and the non-exposed photoresist ismaintained after exposure to provide mold pillars 110).

In some exemplary embodiments, a layer of a thickness in a range of 200μm-1200 μm (e.g. 700 μm) of SU-8 2150 epoxy-type negative photoresist(from MicroChem® of Newton, Mass.) may be spin-coated (or otherwisecoated) onto surface 104A of a substrate 104 comprising a Pyrex™ waferhaving a thickness in a range of 100 μm-500 μm (e.g. 300 μm). Substrate104 and photoresist 102 may be soft-baked for 10 minutes at 65° C. andfor 2.5 hours at 95° C. A dark field mask 106 shaped to define arrays ofcircular-shaped regions transparent to actinic radiation (e.g.apertures) 106A is used to cover masked surface 104B. In someembodiments, the circular-shaped transparent regions 106A have diametersof 20-120 μm (e.g. 40 μm). In some embodiments, transparent regions 106Amay have different shapes (e.g. polygonal). In some embodiments, theedges of such polygonal shaped regions may have sizes in a range of20-120 μm (e.g. 40 μm).

Masked surface 104B of substrate 104 may be exposed to actinic radiationwhich causes the exposed portions of the SU-8 photoresist to formcross-links. In some embodiments, the actinic radiation comprisesultraviolet radiation. In one particular example embodiment, the actinicradiation is 9200 mJ/cm² of ultraviolet light. After the exposure, thesubstrate 104 and the photoresist 102 may be baked for 5 minutes at 65°C. and for 35 minutes at 95° C., then placed in a developer bath for 50minutes to remove the unexposed photoresist 104, then baked for 1 hourat 175° C.

Exposure of the photoresist 102 through transparent regions 106A of mask106 may result in radiation exposure to cone-shaped portions ofphotoresist 102 and may thereby create cone-shaped mold pillars 110after development, wherein such cone-shaped mold pillars 110 comprisebases 110B and tips 110A. This shape may be provided, for example,because of the space (between mask 106 and photoresist 102) provided byexposing photoresist 102 through substrate 104. The bases 110B ofcone-shaped mold pillars 110 may have cross-sectional dimensions thatare greater than the tips 110A of mold pillars 110. This is notnecessary, however. In some embodiments, mold pillars 110 may be shapedsuch that they have sidewall(s) which extend substantially orthogonally(or in the direction of the normal vector) from the surface of substrate104 for at least a portion thereof (e.g. a portion near to bases 110B)and may, optionally, be sharper near tips 110A. In some embodiments,mold pillars 110 may have sidewalls with angles that range from 75 to 90degrees relative to the surface of substrate 104. In some embodiments,mold pillars 110 may have aspect ratios (i.e. ratios of height (e.g.distance between bases 110B and tips 110A) to base dimension (e.g. basediameter, the longest dimension of base 110B and/or the like) that rangefrom 3:1 to 12:1. In other embodiments, mold pillars 110 may have othersidewall angles and other aspect ratios.

As explained in more detail below, the cone-shaped mold pillars 110 ofthe illustrated embodiment may be used to fabricate microneedles withrelatively wide channel openings (e.g. near bases 110B of mold pillars110) and sharp tips (e.g. near tips 110A of cone-shaped mold pillars110). The diameters/edge-lengths of the bases 110B of cone-shaped moldpillars 110 (and the corresponding diameters/edge-lengths of the channelopenings of microneedles fabricated using mold pillars 110) may beapproximately equal to the diameters/edge-lengths of the transparentregions 106A of mask 106.

In some embodiments, substrate 104 upon which mold pillars 110 areformed may be cut (or otherwise separated) into smaller pieces (e.g. 1by 1 cm pieces), with each piece comprising a mold pillar 110 and/or anarray of a plurality of mold pillars 110.

In some embodiments, mold pillars 110 may be further shaped by anysuitable method. For example, the tips 110A of mold pillars 110 may besharpened (e.g. isotropically) using an etching process (e.g. dryetching). In some embodiments, the tips 110A of mold pillars 110 may besharpened asymmetrically—e.g. to have an asymmetric tip shape similar tothe shape 110C of the mold pillar tip 110A shown in FIG. 4A.

In some embodiments, including the exemplary embodiment of FIG. 1C, aprotective layer 112 may be applied to the surfaces of the mold pillars110 and/or to substrate 104 by any suitable method includingsublimation, spray-deposition, condensation, pouring, sputtering,spin-casting, solvent-casting, and/or the like. Such a protective layer112 may increase the strength of mold pillars 110 and/or the bonding ofmold pillars 110 to substrate 104. Protective layer 112 may help to makemold pillars 110 sufficiently durable to be reused multiple times tomake multiple sets of microneedles. Protective layer 112 is optional andnot necessary. In some embodiments, mold pillars 110 may be sufficientlydurable to be reused multiple times to make microneedles even withoutprotective layer 112. Protective layer 112 may comprise any suitablematerial. Protective layer 112 may comprise the same material or adifferent material as mold pillar 110.

FIG. 1C shows an example method for coating mold pillars 110 andsubstrate 104 with a protective layer 112. Protective layer 112 may beapplied by dissolving the material of protective layer 112 in a solventto form a solution, and then casting (e.g. solvent casting and/or spincasting) the solution onto mold pillars 110 and substrate 104. Thesolvent may be evaporated, leaving behind protective layer 112.Protective layer 112 may be cured with light, heat and/or the like.

In one particular and non-limiting embodiment, SU-8 3025 (fromMicroChem® of Newton, Mass.) may be diluted with cyclopentanone to makea 6.7 wt % solution. This solution may be cast (e.g. solvent cast and/orspin cast) onto mold pillars 110 and/or substrate 104 for 20 minutes at95° C. leaving a 30 μm protective layer 112. This protective layer 112may be cured with 900 mJ/cm² of ultraviolet light and baked for 5minutes at 95° C. and for 1 hour at 190° C.

Forming an Electrically-Conductive Layer Over the Mold Pillar

After fabricating or otherwise providing mold pillar 110, the exposedsurface of mold pillar 110 may be coated with an electrically-conductivelayer 114 by any suitable method including, by way of non-limitingexample, sublimation, spray-deposition, condensation, pouring,spin-casting, solvent-casting, sputtering and/or the like. If moldpillar 110 has a protective layer 112, the exposed surface of protectivelayer 112 may be coated with the electrically-conductive layer 114. Insome embodiments, mold pillar 110 or protective layer 112 may be firstcoated with a sacrificial layer (i.e. a layer that may later bedissolved, melted, or otherwise destroyed), and then the exposed surfaceof the sacrificial layer may be coated with conductive layer 114. Insome embodiments, conductive layer 114 itself may provide a sacrificiallayer (as discussed in more detail below).

Conductive layer 114 may comprise any suitable material. In someembodiments, conductive layer 114 comprises one or more conductivepolymers. Conductive layers 114 comprising conductive polymers maycomprise one or more intrinsically or natively conductive polymers (e.g.poly(3,4-ethylene-dioxythiophene)); conductive co-polymers (e.g. thecopolymer of poly(3,4-ethylenedioxythiophene) andpoly(styrene-sulfonate)); and polymers containing conductive particlesto form conductive composite polymer matrices. By way of non-limitingexample, polymers that may be used in conductive composite polymermatrices include:

-   -   poly(methyl methacrylate) (PMMA);    -   poly(vinyl acetate);    -   polyacrylonitrile;    -   poly(vinyl chloride);    -   poly(vinylidene chloride);    -   polyethylene (LDPE, HDPE);    -   polypropylene;    -   polystyrene;    -   polytetrafluoroethylene;    -   biodegradable polymers and copolymers (e.g. poly(lactic acid),        poly(lactic-co-glycolic acid), poly(caprolactone),        polyphosphazenes, and polyanhydrides);    -   biopolymers (e.g. polysaccharides (e.g. chitosan and cellulose),        polypeptides and polynucleotides); and/or    -   the like.

Conductive particles that may be used in conductive composite polymermatrices include carbon black (CB) particles, metal particles (e.g.silver nanoparticles), metal oxide particles, particles comprisingconductive polymers, and/or the like. In some embodiments, conductivelayer 114 may comprise one or more suitable metals or alloys thereof.

FIG. 1D shows an example method for coating one or more mold pillars 110with a conductive layer 114. In the illustrated embodiment, mold pillars110 comprise protective layer 112, although (as discussed above), thisis not necessary and conductive layer 114 may be formed over moldpillars 110 without protective layer 112. In some embodiments,conductive layer 114 is solvent-cast. Conductive layer 114 may beapplied by first dissolving the material of conductive layer 114 in asolvent to form a solution, then casting the solution onto mold pillars110 (e.g. onto protective layer 112 in the case of the illustratedembodiment). The solvent may be evaporated, leaving behind conductivelayer 114 on mold pillars 110. In the FIG. 1D embodiment, mold pillars110 are oriented so that they extend away from substrate 104 in adirection that is opposed to the force of gravity—i.e. tips 110A of moldpillars 110 are located above substrate 104. The force of gravity maycause the conductive layer solution to form a relatively thin layer attips 110A and a relatively thick layer closer to bases 110B.Consequently, in some embodiments, conductive layer 114 may berelatively thin or even absent at tips 110A. The solvent-castingparameters (e.g. concentration, temperature, dew point, evaporationrate, humidity, etc.) may be adjusted to control the thickness ofconductive layer 114 (e.g. the thickness of conductive layer 114 betweentips 110A and bases 110B of mold pillars 110).

In some exemplary embodiments, the conductive layer 114 may comprisePMMA (from Polysciences® of Warrington, Pa.), with molecular weight of25 kDa, seeded with carbon black (CB, VULCAN® XC72R, from Cabot®Corporation of Boston, Mass.), with a primary particle size of about 150nm. A PMMA/CB solution/suspension may be prepared by adding 0.3 g ofPMMA and 0.135 g of CB to a carrier fluid comprising 5 g ofN-methyl-2-pyrrolidone (NMP). In some embodiments, other suitablecarrier fluids may be used. By way of non-limiting example, suitablecarrier fluids may include dimethylformamide (DMF), dimethylsulfoxide(DMSO), longer chain alcohols including 1-octanol, and/or the like.

A surfactant comprising 0.015 g of sodium dodecyl sulfate (SDS, fromSigma-Aldrich® of Oakville, ON) may be added to the conductive polymersolution/suspension. The solution/suspension may be placed in anultrasonic bath for 30 minutes. The resulting fluid may have a solidconcentration of 9 wt % with CB accounting for 30% of the total solidcontent. This fluid may be applied to mold pillars 110 (e.g. ontoprotective layer 112 in the case of the illustrated embodiment) andsubstrate 104 and allowed to evaporate to leave behind a conductivelayer comprising a polymer matrix of PMMA and CB.

The surfactant may help to prevent the formation of CB particle clustersand may thereby result in a relatively uniform distribution of the CBparticles in the solution/suspension. Uniform suspension of the CBparticles in the solution/suspension may result in uniform distributionof the CB particles within the PMMA polymer matrix once the material iscast onto mold pillars 110 and substrate 104. The uniform distributionof CB particles within the PMMA polymer matrix may result in conductivelayer 114 having uniform conductivity. As discussed in more detailbelow, this uniform conductivity of conductive layer 114 may in turnfacilitate deposition, by electroplating, of a uniform metal layer 118over conductive layer 114.

Any suitable surfactant may be used in the conductive polymersolution/suspension. By way of non-limiting example, suitablesurfactants may comprise:

-   -   non-ionic surfactants including:        -   polyoxyethylene glycol octylphenol ethers (Triton X-100),        -   glucoside allyl ethers (lauryl glucoside),        -   sorbitan alkyl esters (spans),        -   copolymers of polyethylene glycol,        -   polypropylene glycol (poloxamers), and/or        -   the like;    -   anionic surfactants including:        -   sodium dodecyl sulfate,        -   ammonium lauryl sulfate,        -   sodium lauryl sulfate,        -   alkyl-aryl ether phosphates,        -   alkyl ether phosphates,        -   dioctyl sodium sulfosuccinate,        -   perfluorooctanesulfonate, and/or        -   the like;    -   cationic surfactants including:        -   cetyl trimethylammonium bromide,        -   cetylpyridinium chloride, and        -   dimethyldioctadecylammonium chloride, and/or        -   the like; and    -   zwitterionic surfactants including:        -   lecithin (phosphatidyl choline),        -   CHAPS            (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate),            and/or        -   the like; and/or    -   the like.

In some embodiments, a substance may be applied to mold pillars 110and/or substrate 104 (or protective layer 112 or the sacrificial layer,if present) to improve surface adhesion before applying conductive layer114. For example, in one particular example embodiment, 20 μl ofhexamethyldisilazane (HMDS, from Sigma-Aldrich® of Oakville, ON) may beapplied to mold pillars 110 (e.g. onto protective layer 112 in the caseof the illustrated embodiment) and substrate 104 at room temperature.Then, 40 μl of the 9 wt % PMMA/CB mixture may be deposited onto moldpillars 110 and substrate 104 and then baked for 3 hours at 80° C. toevaporate the NMP and fully dry the PMMA/CB mixture. The resulting layerof PMMA/CB may be 100 μm thick on substrate 104 and may graduallydecrease in thickness towards tips 110A of mold pillars 110.

In some embodiments conductive layer 114 may be apertured to provideapertured conductive layer 114A. In this description, use of the termconductive layer 114 may (but need not necessarily) include aperturedconductive layer 114A, as the context dictates. Apertured conductivelayer 114A may be used to fabricate hollow microneedles (i.e.microneedles with apertures therethrough). A solid (i.e. non-apertured)conductive layer 114 may be used to fabricate solid (i.e. non-apertured)microneedles.

Any suitable method may be used to form apertured conductive layer 114Ahaving or defining one or more apertures 117 therethrough. Any suitablemethod may be used to make or create one or more apertures 117 in aconductive layer 114 that is already formed to provide aperturedconductive layer 114A.

An aperture 117 through apertured conductive layer 114A may be locatedanywhere on apertured conductive layer 114A. In some embodiments,apertures 117 are located on apertured conductive layer 114A in regionscorresponding to mold pillars 110. For example, apertures 117 may extendthrough apertured conductive layer 114A to expose the surfaces of moldpillars 110 or may extend through apertured conductive layer 114A inregions corresponding to (e.g. covering) mold pillars 110, as opposed toregions between mold pillars 110. In some embodiments, an aperture 117may be located at the tip 110A of mold pillar 110. In some embodiments,an aperture 117 may be symmetrically shaped at tip 110A of mold pillar110. In some embodiments, an aperture 117 may be asymmetrically shapedat tip 110A of mold pillar 110 in a manner similar to that shown in FIG.4B.

In some embodiments, an aperture 117 may be made in an already-formedconductive layer 114 using a suitable etching technique to provideapertured conductive layer 114A. Suitable etching techniques may includechemical etching, physical etching, plasma etching, reactive ion etchingand/or the like. In some embodiments, an aperture 117 may be made in analready-formed conductive layer 114 using laser ablation to provideapertured conductive layer 114A.

FIG. 1E shows an example method for removing conductive layer 114 fromtips 110A of mold pillars 110 to form apertures 117 that extend throughconductive layer 114 in regions corresponding to mold pillars 110 (moreparticularly, to tips 110A of mold pillars 110) and to thereby provideapertured conductive layer 114A. Conductive layer 114 may be bombardedby ions 116 in the general direction shown by arrows in FIG. 1E. Ions116 may wear away conductive layer 114 until apertures 117 are formedand tips 110A of mold pillars 110 (or the portions of protective layer112 covering tips 110A) are exposed to thereby provide aperturedconductive layer 114A. The etching process may cause tips 110A to havehigher temperatures than other portions of mold pillars 110. Moldpillars 110 may have poor thermal conductivity and this may contributeto the temperature differential. The higher temperature of tips 110A maycause an increased etching rate at tips 110A compared to at otherportions of mold pillars 110.

In some embodiments, the portion of conductive layer 114 covering thetip 110A of a mold pillar 110 (or some other portion of conductive layer114 that covers mold pillar 110) may be removed to make apertures 117 byplasma etching to thereby provide apertured conductive layer 114A. Byway of non-limiting example, the plasma may comprise O₂/CF₄ (O₂ flowrate: 80 sccm; CF₄ flow rate: 20 sccm; pressure: 500 mTorr; temperature:25° C.; power: 200 W). The plasma may be applied for a suitable duration(e.g. 200 seconds) or until conductive layer 114 is removed from the tip110A of mold pillar 110 to provide apertures 117 and to thereby provideapertured conductive layer 114A.

In some embodiments, portions of conductive layer 114 may be removed tomake apertures 117 (and to thereby provide apertured conductive layer114A) by mechanical grinding, laser micromachining or by localizedheating.

In some embodiments, conductive layer 114 may comprise aphoto-patternable polymer and portions of conductive layer 114 may beremoved to form apertures 117 by photolithography to thereby provideapertured conductive layer 114A.

In some embodiments, conductive layer 114 may be applied usingsolvent-casting and various solvent-casting parameters (e.g.concentration, temperature, dew point, evaporation rate, humidity, etc.)may be adjusted so that portions of mold pillars 110 are not coated withconductive layer 114 when the solvent is evaporated—i.e. such thatapertures 117 are formed through conductive layer 114 as conductivelayer 114 is applied to mold pillars 110 to thereby provide aperturedconductive layer 114A. For example, the concentration of a polymer or asurfactant in the conductive polymer solution used to apply conductivelayer 114 may be adjusted so that conductive layer 114 does not form inregions corresponding to the tips 110A of mold pillars 110, therebyproviding apertures 117 through conductive layer 114 in the vicinitiesof tips 110A to thereby provide apertured conductive layer 114A.

In some embodiments, a portion of the surface of a mold pillar 110 maybe chemically or physically modified to change its wetting behavior, sothat a solvent-cast conductive layer 114 may be formed with an aperture117 to thereby provide apertured conductive layer 114A. If, for example,conductive layer 114 is solvent-cast using a polar solvent, then anon-polar coating (not shown) may be applied to the tip 110A of moldpillar 110 (or to some other region of mold pillar 110 where it isdesired to provide an aperture 117), so that conductive layer 114 doesnot wet (or adhere to) the region (e.g. the tip 110A) of mold pillar 110that is coated with the non-polar coating. If, for example, a conductivelayer 114 is solvent-cast using a non-polar solvent, then a polarcoating (not shown) may be applied to the 110A tip of mold pillar 110(or to some other region of mold pillar 110 where it is desired toprovide an aperture 117), so that conductive layer 114 does not wet (oradhere to) the region (e.g. the tip 110A) of mold pillar 110 that iscoated with the polar coating.

In some embodiments, where conductive layer 114 is applied by solventcasting using a water-based solvent, hydrophobic nanoparticles may bedeposited onto the tip 110A of mold pillar 110 (or to some other regionof mold pillar 110 where it is desired to provide an aperture 117)before conductive layer 114 is applied to mold pillar 110. Any suitabletype of hydrophobic material may be used including, by way ofnon-limiting example, poly(ethylene-co-tetrafluoroethylene),poly(chlorotrifluoro-ethylene), poly(vinylidene fluoride),poly(vinylidene fluoride-co-hexafluoropropylene), and/or the like.Before the hydrophobic nanoparticles are deposited, the tip 110A of moldpillar 110 may be coated with a thin layer of SU-8, which may help thehydrophobic nanoparticles to adhere to tip 110A. The SU-8 may be appliedby stamping, for example.

In one example embodiment, a dry 300 nm diameter polytetrafluoroethylene(PTFE) nanoparticle powder may be mixed into ethanol at a 1:50 weightratio to form a suspension. The suspension may be deposited onto a stampusing an airbrush. The stamp may comprise a soft piece ofpolydimethylsiloxane (PDMS), fabricated using standard soft lithography.The airbrush's suspension and airflow rate and the distance between theairbrush and the stamp may be adjusted to ensure that the atomizeddroplets expelled by the airbrush evaporate upon reaching the stamp. Thecoated mold pillar 110 may be baked for 2 minutes at 100° C., then auniform contact may be made between the stamp and the tip of the moldpillar for 10 seconds.

It will be appreciated that in some embodiments, where conductive layer114 is applied by solvent casting using a non-polar solvent, oleophobicnanoparticles may be deposited onto the tip 110A of mold pillar 110 (orto some other region of mold pillar 110 where it is desired to providean aperture 117) before conductive layer 114 is applied to mold pillar110, thereby facilitating the formation of apertured conductive layer114A in an analogous process.

Depositing Metal Layer(s) Over Electrically-Conductive Layer to Providea Microneedle

One or more metal layers 118 may be deposited onto conductive layer 114using any suitable method including electroplating, sputtering, and/orthe like. In currently preferred embodiments, one or more metal layers118 are applied to apertured conductive layer 114A using anelectroplating technique which creates one or more correspondinglyapertured metal layers 118A. In this description, use of the term metallayer 118 may (but need not necessarily) include apertured metal layer118A, as the context dictates. Metal layer 118 may comprise any suitablemetal including, by way of non-limiting example, cobalt, nickel,chromium, manganese, iron, gold, copper, lead, ruthenium, rhodium,palladium, silver, mercury, rhenium, titanium, niobium, tantalum,osmium, iridium, platinum, combinations thereof; and/or the like. Metallayer 118 may provide desirable structural strength to a microneedle 120fabricated therefrom.

In some embodiments, multiple metal layers 118 may be deposited ontoelectrically-conductive layer 114. In some embodiments, metals A, B, andC, may be deposited in sequence, so only metals A and C will be exposedin the completed microneedle (assuming that electrically conductivelayer 114 is partially or completely removed when the microneedle isremoved from mold pillar 110). The encapsulated metal B may be astructural metal and may comprise nickel, for example. The exposedmetals A and C may comprise biocompatible metals. The exposed metals Aand C may be the same as one another or different from one another.Non-limiting examples of biocompatible metals include: gold, platinum,titanium, CoCr, 316L stainless steel, cobalt-chromium, titanium,titanium-based implant alloys which rely on their passivation by a thinlayer of oxide, alloys thereof and/or the like.

FIG. 1F shows an example method for coating conductive layer 114 with ametal layer 118 by electroplating. More particularly, FIG. 1F shows amethod for electroplating a metal layer 118 onto apertured conductivelayer 114A to provide apertured metal layer 118A. Conductive layer 114may be placed in a solution 116 containing metal ions. Conductive layer114 may be connected as one of two electrodes in solution 116. A voltagemay be applied between the electrodes and the metal ions in solution 116may be electroplated onto conductive layer 114, thereby forming metallayer 118. If conductive layer 114 has an aperture 117 (as is the casein apertured conductive layer 114A in the illustrated embodiment), metalions are not deposited onto or into aperture 117, thereby forming anapertured metal layer 118A having aperture 117. As mentioned above, inthe FIG. 1F embodiment, apertured conductive layer 114A has apertures117 at tips 110A of mold pillars 110 and, consequently, the FIG. 1Felectroplating process forms an apertured metal layer 118A is formedwith apertures 117 at tips 110A of mold pillars 110. Metal layer 118 mayprovide an array of microneedles 120.

In one embodiment, conductive layer 114 may be placed into anelectroplating solution. The electroplating solution may comprise nickelchloride, nickel sulfate, and boric acid. Conductive layer 114 may bepositioned parallel to and 2.5 cm away from a pure nickel anode.Conductive layer 114 may act as a cathode and may be connected to apower supply by a suitable electrical connection (e.g. a wire).Conductive layer 114 may have a lower conductivity than the electricalconnection, and the electrical connection may be kept, for the mostpart, out of the solution to prevent nickel from accumulating on theelectrical connection. The power supply may provide a constant currentof 2 mA for 150 minutes. A metal layer 118 of nickel may thereby beformed over conductive layer 114. In some embodiment, metal layer 118has a thickness in a range of 10 to 200 μm (e.g. 70 μm). In otherembodiments, metal layer 118 may have a wider thickness range.

In one embodiment, 0.2 mm diameter platinum wires (from Alfa Aesar® ofWard Hill, Mass.) may be used as anodes. In other embodiments, wiresmade of other suitable materials may be used as anodes. A Kenwood®PR18-1.2 A power supply (from Davis Instruments™ of Baltimore, Md.) maybe used to electroplate a first metal layer on the conductive layer.Then, a layer of gold may be electroplated onto the first metal layerusing a solution comprising a phosphate buffer at pH7, 0.17 M of H₃PO₄,0.07 M of KH₂PO₄, and 0.07 M of KAu(CN)₂. The gold may be electroplatedfor 5 minutes at a current density at 102 A/m². The final thickness ofthe gold layer may be in a range of 0.05 to 10 μm (e.g. 3 μm).

Removing Microneedle from the Mold Pillar

Microneedle 120 provided by metal layer 118 may be removed from moldpillar 110 by any suitable method. By way of non-limiting example:

-   -   mold pillar 110 may be at least partially dissolved or otherwise        depleted until metal layer 118 (and microneedle 120) can be        removed from mold pillar 110;    -   conductive layer 114 may be at least partially dissolved or        otherwise depleted until metal layer 118 (and microneedle 120)        can be removed from mold pillar 110;    -   conductive layer 114 may have a weak surface bond with metal        layer 118, allowing metal layer 118 (and microneedle 120) to be        removed mechanically from mold pillar 110;    -   conductive layer 114 may be softened or melted by heat treatment        until metal layer 118 (and microneedle 120) can be removed        mechanically;    -   a sacrificial layer may have been formed between mold pillar 110        and conductive layer 114 and:        -   the sacrificial layer may be at least partially dissolved,            depleted or destroyed to permit microneedle 120 (including            metal layer 118 and possibly some or all of conductive layer            114) to be removed from mold pillar 110;        -   the sacrificial layer may have a weak surface bond with            conductive layer 144 to permit mechanical removal of            microneedle 120 (including metal layer 118 and possibly some            or all of conductive layer 114) from mold pillar 110;        -   the sacrificial layer may be softened or melted by heat            treatment to permit microneedle 120 (including metal layer            118 and possibly some or all of conductive layer 114) to be            removed from mold pillar 110; and/or    -   the like.

The sacrificial layer may be conductive or non-conductive. Thesacrificial layer may be made of any suitable material including silicondioxide, silicon nitride, silicon germanium, and polysilicon. It may bedeposited by any suitable method including sublimation, spraydeposition, chemical vapor deposition, condensation, pouring,solvent-casting, sputtering, and/or the like.

In embodiments where mold pillar 110 is left intact (or substantiallyintact) after microneedle 120 is removed, mold pillar 110 may be reusedto fabricate additional microneedles.

Where an apertured, electrically-conductive layer 114A was used and acorresponding apertured metal layer 118A is formed upon the aperturedelectrically conductive later, the removed microneedle 120 may comprisea hollow (or apertured) microneedle 120 (e.g. a microneedle 120 throughwhich fluid may travel). Where a non-apertured, electrically-conductivelayer 114 was used, the removed microneedle 120 may comprise anon-apertured microneedle. In some embodiments, a non-aperturedmicroneedle 120 may remain attached to mold pillar 110 and may not beremoved from mold pillar 110 prior to use.

FIG. 1G shows an example method for removing an array of microneedles120 from mold pillars 110. In the FIG. 1G, conductive layer 114comprises a sacrificial layer which is at least partially destroyed toremove microneedles 120 from mold pillars 110. Conductive layer 114 maybe at least partially dissolved using a suitable solvent (e.g. the samesolvent which was used to solvent-cast conductive layer 114 in step ofFIG. 1D). Once conductive layer 114 is partially dissolved, the array ofmicroneedles 120 may be removed from mold pillars 110. Microneedles 120may comprise apertured (or so-called hollow) microneedles 120. As shownin FIG. 1G, microneedles 120 may comprise lumens 120A (which are formedat bases 110B of mold pillars 110), apertures/nozzles 120B (which areformed at tips 110A of mold pillars 110), outside surfaces 120C, andinside surfaces 120D.

In some embodiments, the array of microneedles 120 may be removed frommold pillars 110 by placing conductive layer 114 in an ultrasonic bathof NMP for 60 minutes or until conductive layer 114 dissolvessufficiently for removal of the array of microneedles 120.

A microneedle 120 may have its outside and/or inside surfaces 120C, 120Dcleaned (e.g. to remove any remaining electrically-conductive layer114). A microneedle 120 may have its outside and/or inside surfaces120C, 120D coated with any suitable coating including polymer coatingsand/or metal coatings. Such coatings may be applied by any suitablemethod including, by way of non-limiting example, electroplating,sputtering, evaporation, chemical vapor deposition and/or the like. Suchcoatings may be applied before or after microneedle 120 is removed frommold pillar 110. Such coatings may modify the surface properties ofmicroneedle 120. For example, such coatings may make the surface(s) ofmicroneedle 120 hydrophobic, hydrophilic, biocompatible,electrically-insulating and/or the like. Biocompatible coatings may beuseful for applications where microneedle 120 is used in applicationswhich puncture the skin or are otherwise used inside of the body of ahuman or other animal. Non-limiting examples of biocompatible metalsinclude: gold, platinum, titanium, CoCr, 316L stainless steel,cobalt-chromium, titanium, titanium-based implant alloys which rely ontheir passivation by a thin layer of oxide, alloys thereof and/or thelike. Non-metallic biocompatible coatings could also be used, forexample, poly(methylmetacrylate). An electrically insulating coating maybe beneficial, for example, when microneedle 120 is used as part of anelectrochemical sensor. An electrically insulating coating may compriseany suitable material including polyethylene terephthalate,polytetra-fluoroethylene, polyethylene, poly(methyl methacrylate),polylactide, polyglycolide, poly(lactide-co-glycolide) and/or the like.

As discussed above, metal layer 118 provides structural strength tomicroneedles 120 fabricated therefrom. In some embodiments, microneedles120 may be strong enough to pierce human skin. Prototype arrays ofmicroneedles 120 were fabricated using the example method depicted inFIGS. 1A-1G. The prototype arrays of microneedles 120 were subject to aseries of mechanical compression tests and the results of these testswere compared with literature data. A vertical compressive load wasapplied to a prototype array of microneedles 120 at a constant velocityof 5 μm/second. Force vs. displacement data were obtained for analysisof failure loads. After each compression test the microneedles 120 werevisually inspected to see if the microneedle shafts buckled or if themicroneedle tips collapsed.

Five compression tests were conducted and the average failure load was4.2±0.61 N. For a microneedle 120 with a tip diameter of less than 50 μm(as is the case with the prototype microneedles 120 subjected to themechanical compression tests), typical forces associated with thepenetration of microneedles 120 into human skin are well below 1 N. Thefailure load of the prototype microneedles was well above 1 N, andtherefore the prototype microneedles are strong enough to be insertedinto human skin without breaking.

FIG. 2 is a schematic illustration of a method 200 for fabricating ametallic microneedle 120 according to an example embodiment. Method 200commences in block 202 which comprises fabricating or otherwiseproviding a mold pillar 110. The block 202 mold pillar 110 may befabricated or otherwise provided using any of the features, combinationsof features or sub-combinations of features described above inconnection with providing mold pillars 110 (including, for example, thedescription of FIGS. 1A, 1B and/or 1C). The block 202 mold pillar 110may comprise a protective layer 112, which may be considered part ofmold pillar 110.

Method 200 then proceeds to block 204 which comprises forming anapertured electrically conductive layer 114A over the block 202 moldpillar 110. Forming the apertured electrically conducting layer 114A maycomprise using any of the features, combinations of features orsub-combinations of features described above in connection with formingapertured electrically conductive layer 114A (including, for example,the description of FIGS. 1D and/or 1E). In some exemplary embodiments,apertured electrically conducting layer 114A comprises electricallyconductive polymer, which may be applied in block 204 by solventcasting. As discussed above, apertures 117 may be formed on electricallyconductive layer 114 as conductive layer 114 is applied to the block 202mold pillar 110 to provide apertured electrically conductive layer 114Aor after conductive layer 114 is applied to the block 202 mold pillar110 to provide apertured electrically conductive layer 114A.

Method 200 then proceeds to block 206 which comprises depositing a metallayer 118 over the block 204 apertured electrically conductive layer114A. Depositing the metal layer 118 in block 206 may comprise using anyof the features, combinations of features or sub-combinations offeatures described above in connection with depositing metal layer 118(including, for example, the description of FIG. 1F). In some exemplaryembodiments, metal layer 118 is applied to conductive layer 114 using anelectroplating technique. Where conductive layer 114 comprises anapertured conducting layer 114A, electroplating causes the deposition ofa corresponding apertured metal layer 118A. In some embodiments, block206 comprises depositing multiple metal layers 118.

Method 200 may comprise an optional block 208 which involves removingmicroneedle 120 from mold pillar 110. Removing microneedle 120 inoptional block 208 may comprise any of the features, combinations offeatures or sub-combinations of features described above in connectionwith removing microneedle 120 from mold pillar 110 (including, forexample, the description of FIG. 1G). In some exemplary embodiments, theelectrically conductive polymer used to provide apertured conductivelayer 114A is at least partially dissolved to permit the block 208removal of microneedle 120 from mold pillar 110.

FIG. 3 is a schematic diagram showing a method 300 for fabricating ametallic microneedle 120 according to an example embodiment. Method 300commences in block 302 which comprises fabricating or otherwiseproviding a mold pillar 110. Block 302 may be similar to block 202 ofmethod 200 described above. The block 302 mold pillars 110 may compriseelectrically conductive layers 114 and block 302 may comprise forming anelectrically conductive layer 114 on mold pillar 110 in accordance withany of the features, combinations of features or sub-combinations offeatures described above in connection with forming electricallyconductive layer 114 (including, for example, the description of FIGS.1D and/or 1E).

In some embodiments, method 300 comprises optional block 303 whichcomprises forming an electrically conductive layer 114 over the block302 mold pillar 110. Forming the block 303 electrically conductive layer114 may comprise using any of the features, combinations of features orsub-combinations of features described above in connection with formingelectrically conductive layer 114 (including, for example, thedescription of FIGS. 1D and/or 1E). In some exemplary embodiments,electrically conductive layer 114 comprises electrically conductivepolymer, which may be applied in block 303 by solvent casting. Asdiscussed above, apertures 117 may be formed on electrically conductivelayer 114 as conductive layer 114 is applied to the block 302 moldpillar 110 to provide apertured electrically conductive layer 114A orafter conductive layer 114 is applied to the block 302 mold pillar 110to provide apertured electrically conductive layer 114A.

Method 300 then proceeds to block 304 which comprises depositing a metallayer 118 over the block 302 mold pillar 110 and/or the block 303electrically conductive layer 114. Depositing the metal layer 118 inblock 304 may comprise using any of the features, combinations offeatures or sub-combinations of features described above in connectionwith depositing metal layer 118 (including, for example, the descriptionof FIG. 1F). In some exemplary embodiments, where the block 302 moldpillar comprises an electrically conductive layer 114, metal layer 118may be applied to the block 302 mold pillar using an electroplatingtechnique. Where the block 302 mold pillar 110 comprises an aperturedconducting layer 114A, electroplating causes the deposition of acorresponding apertured metal layer 118A. In some embodiments, block 304comprises depositing multiple metal layers 118.

Method 300 then proceeds to block 306 which comprises removingmicroneedle 120 from mold pillar 110. Removing microneedle 120 in block306 may comprise any of the features, combinations of features orsub-combinations of features described above in connection with removingmicroneedle 120 from mold pillar 110 (including, for example, thedescription of FIG. 1G). In some exemplary embodiments, an electricallyconductive polymer used to provide a conductive layer 114 on the block110 mold pillar is at least partially dissolved to permit the block 306removal of microneedle 120 from mold pillar 110.

Method 300 then proceeds to block 308 which comprises depositing asecond metal layer 118 over the block 302 mold pillar to provide asecond microneedle. Block 308 may comprise using at least a portion ofthe block 302 mold. Block 308 may optionally comprise forming anelectrically conductive layer 114 over the block 302 mold pillar 110(and possibly over any remnants of the block 303 electrically conductivelayer 114). Forming such electrically conducting layer may compriseusing any of the features, combinations of features or sub-combinationsof features described above in connection with forming electricallyconductive layer 114 (including, for example, the description of FIGS.1D and/or 1E). Applying the second metal layer over the mold pillar inblock 308 may comprise using any of the features, combinations offeatures or sub-combinations of features described above in connectionwith depositing metal layer 118 (including, for example, the descriptionof FIG. 1F).

FIG. 5 is a schematic diagram showing a method 400 for fabricating ametallic microneedle 120 according to an example embodiment. Method 400commences in block 402 which comprises fabricating or otherwiseproviding a mold pillar 110. Block 402 may be similar to block 202 ofmethod 200 described above.

Method 400 then proceeds to block 404 which comprises forming anelectrically conductive layer 114 comprising an electrically conductivepolymer over the block 402 mold pillar 110. Forming the block 404electrically conductive layer 114 may comprise using any of thefeatures, combinations of features or sub-combinations of featuresdescribed above in connection with forming electrically conductive layer114, where electrically conductive layer 114 comprises an electricallyconductive polymer (including, for example, the description of FIGS. 1Dand/or 1E). In some exemplary embodiments, electrically conductive layer114 may be applied in block 404 by solvent casting. As discussed above,apertures 117 may be formed on electrically conductive layer 114 aselectrically conductive layer 114 is applied to the block 402 moldpillar 110 to provide apertured electrically conductive layer 114A orafter electrically conductive layer 114 is applied to the block 402 moldpillar 110 to provide apertured electrically conductive layer 114A.

Method 400 then proceeds to block 406 which comprises depositing a metallayer 118 over the block 404 electrically conductive polymer layer 114.Depositing the metal layer 118 in block 406 may comprise using any ofthe features, combinations of features or sub-combinations of featuresdescribed above in connection with depositing metal layer 118(including, for example, the description of FIG. 1F). In some exemplaryembodiments, metal layer 118 may be applied to the block 404electrically conductive polymer layer 114 using an electroplatingtechnique. Where the block 404 electrically conductive polymer layer 114comprises an apertured electrically conductive polymer layer 114A,electroplating causes the deposition of a corresponding apertured metallayer 118A. In some embodiments, block 406 comprises depositing multiplemetal layers 118.

In some embodiments, method 400 comprises optional block 408 whichcomprises removing microneedle 120 from mold pillar 110. Removingmicroneedle 120 in block 408 may comprise any of the features,combinations of features or sub-combinations of features described abovein connection with removing microneedle 120 from mold pillar 110(including, for example, the description of FIG. 1G). In some exemplaryembodiments, an electrically conductive polymer used to provide aconductive layer 114 on the block 110 mold pillar is at least partiallydissolved to permit the block 408 removal of microneedle 120 from moldpillar 110.

Application 1: Delivery Devices

Microneedles 120 may be used for delivery of agents into human or animaltissue, or into plants or soil. Microneedles 120 may be used to deliverany suitable agent including drugs, compounds, particles, andsuspensions. Microneedles 120 may be used to deliver vaccines,neurotoxins such asBotox®, and agents for allergy tests.

Hollow (i.e. apertured) microneedles 120 may be used for directinjection of agents. For transdermal injections, a hollow microneedle120 (or an array of hollow microneedles 120) may pierce the outermostlayer of skin (the stratum corneum) and release an agent into the dermalor the epidermal tissue of the skin. In some embodiments, a microneedle120 may be inserted into skin without damaging or touching nerves sothat the insertion is painless or less painful than the insertion of atraditional hypodermal needle. In some embodiments, microneedles 120 maybe inserted without touching blood vessels in the dermis.

An array of microneedles 120 (or a single microneedle 120) may beattached to a container, such as a conventional syringe or amicroreservoir, containing an agent. A membrane may be moved or deformedto pressurize the agent, thereby forcing it out through the lumens ofthe microneedles 120.

A 500 μm tall prototype microneedle 120 fabricated using the methoddepicted in FIGS. 1A-1G was used to inject fluorescent beads intopigskin. The microneedle 120 was bound to the tip of a conventional 1 mlsyringe. The syringe was filled with a 0.01 wt % suspension of 2.28 μmfluorescent beads in water. The microneedle 120 was pressed against theskin, and a force of approximately 2 N was applied to the syringeplunger for 5 minutes. The skin surface near the injection site waswashed with water and dried with a wipe. A Nikon® Eclipse® C1 confocalmicroscope (Melville, N.Y.) was used to scan the distribution of thefluorescent beads inside the skin. The confocal scan of the injectionsite indicated delivery of the fluorescent beads to a depth of 250 μminto the skin. A control test was performed by applying a fluorescentbead solution to the surface of pigskin for 10 minutes, washing theskin, and then taking a confocal scan of the skin. The control test didnot show any fluorescent microspheres below the skin surface. Thissuggests that pigskin is not permeable to the fluorescent beads and thatthe prototype microneedle 120 may be useful for transdermal delivery ofdrugs, including suspensions.

A 500 μm tall prototype nickel microneedle 120 fabricated using themethod depicted in FIGS. 1A-1G was used to inject a fluorescentchemotherapeutic drug (doxorubicin) into pigskin. A backing plate of themicroneedle was bonded to a drug container that was connected to aconventional syringe via a flexible plastic capillary tube. The syringewas filled with a 174 μM solution of doxorubicin in water. The syringewas placed in a commercial syringe pump system (from KD Scientific™ ofHolliston, Mass.). The microneedle 120 was applied to a shaved pigskinsample. The pump was set to push the plunger to generate a constant flowrate of 0.2 μL/minute for 3 minutes. This flow rate was selected basedon a study investigating the efficiency of transdermal drug injectionusing silicon microneedles (U. O. Häfeli, et al., (2009), Biomed.Microdevices, Vol. 11, pp. 943-950) which found an average delivery rateof 0.2 μL/minute through each needle in an injection trial. After theinjection, the skin was cleaned and then scanned using confocalmicroscopy. The confocal scans showed penetration of the doxorubicindown to a depth of approximately 130 μm.

In some embodiments, an agent is embedded within the structure of amicroneedle 120 and/or coated on the surface of a microneedle 120, andinsertion of the microneedle 120 into the skin causes the agent to betransferred to the skin. The microneedle 120 may be a solid or hollowmicroneedle 120. The microneedle 120 may not need to be removed from themold pillar with which it was formed.

Application 2: Perforation Devices

Microneedles 120 may be used as perforation devices for perforating(e.g. creating holes, scratches, scars, etc.) in skin (e.g. the stratumcorneum). Solid or hollow microneedles 120 may be used. The microneedles120 may be applied to skin by any suitable method including stamping androlling (e.g. attaching an array of microneedles 120 to a roller androlling the roller across an area of skin).

An agent may be applied to an area of skin before and/or after the areaof skin is perforated. The perforations in the skin may increase thepermeability of the skin and may enhance the uptake of the agent throughthe skin.

Vacuum suction devices may be used to extract biological fluids (e.g.interstitial fluid and blood) from perforated skin.

Application 3: Sensing

Microneedles 120 may be used to take up one or more agents. For example,an array of hollow microneedles 120 may be used to penetrate skin andtake up a bodily fluid (e.g. an interstitial fluid containing ananti-cancer drug). The fluid may be actively drawn into the microneedles120 by any suitable method including pressure, electric fields,capillary forces, and diffusion through a carrier liquid within themicroneedles 120. The fluid may then be directed to one or more sensingregions. The fluid may be transported to the sensing regions viachannels. The sensing regions may be located on the side of themicroneedle array opposite from the side that the fluid enters themicroneedle array. The sensing regions may comprise any suitablesensors, including optical and electrochemical sensors.

Application 4: Material Deposition

Microneedles 129 may be used to deposit material (e.g. fluids, powders,etc.). Microneedles 120 may act as nozzles. Droplets of fluid may beejected from individual microneedle openings (in a manner similar toinkjet printing). Alternatively, jets of fluid may be ejected fromindividual microneedle openings. In the case of a relatively viscousfluid, the ejection may form a relatively viscous jet. Material may beejected using any suitable method including the application of pressureand electric fields.

Material may be ejected from an array of microneedles 120. Material maybe ejected from all the microneedles 120 of the array simultaneously.The microneedles 120 may be actuated individually to control theejection of material from each individual microneedle 120. Themicroneedles 120 may be actuated in groups to control the ejection ofmaterial from each group of microneedles 120. The material ejected fromeach microneedle 120 may be the same or different as the materialejected from other microneedles 120. The material ejected from eachmicroneedle 120 may be changed over time. The material ejected from themicroneedles 120 may be deposited onto a substrate and may form apatterned structure.

Application 5: Electrodeposition

Microneedles 120 may be used to deposit material through electrospinningor electro spray deposition. An electric field may be applied between amaterial to be ejected and a target substrate (or an electrode beneaththe target substrate). The material may be contacted by an electrodebefore it exits a microneedle 120, or the microneedle 120 may be used asan electrode. The material may also be driven by a positive displacementpump. The material may break up into droplets as it exits themicroneedle 120, or it may form a jet. The electric field may cause thejet to undergo a whipping motion, stretching the jet. If the material isa polymer solution, the solvent may evaporate and leave behind a verythin fiber.

Application 6: Combustion

A microneedle 120 may be used as a fuel injector for liquid or gas fuel.The fuel may be ejected through the microneedle 120. The fuel maycomprise a mixture of materials that can react with each other. The fuelmay react with the surrounding air or with a substance exiting othermicroneedles 120. The fuel may be ignited.

Application 7: Tattoos

Microneedles 120 may be used to create tattoos. Relatively shortmicroneedles 120 may be used to create temporary tattoos. Relativelylong microneedles 120 may be used to create permanent tattoos.

Application 8: Imaging

Microneedles 120 may be embedded into a material or tissue and imaged.For example, a microneedle array may form part of a medical device suchas an instrument or an implant, and this device may be inserted orimplanted into tissue. The microneedle array may be imaged by anysuitable imaging process including radiological imaging, x-ray imaging,computed tomography imaging, fluoroscopy/angiography imaging, and anycombination thereof. Metal microneedles 120 may have good x-ray contrastproperties.

While a number of exemplary aspects and embodiments have been discussedabove, those of skill in the art will recognize certain modifications,permutations, additions and sub-combinations thereof. It is thereforeintended that the following appended claims and claims hereafterintroduced are interpreted to include all such modifications,permutations, additions and sub-combinations as are within their truespirit and scope.

What is claimed is:
 1. A method for fabricating microneedles, the methodcomprising: fabricating a mold pillar; forming one or more coatinglayers on the mold-pillar, the one or more coating layers comprising anelectrically-conductive polymer layer; and depositing a metal layer overthe electrically-conductive polymer layer to provide a firstmicroneedle; wherein, after forming the one or more coating layers onthe mold pillar, a thickness of the one or more coating layers whichcoat the mold pillar is relatively thick in regions closer to thesubstrate and relatively thin in regions more distal from the substrate.2. A method according to claim 1 wherein forming the one or more coatinglayers on the mold pillar comprises depositing a protective layer overthe mold pillar to thereby coat the mold pillar with the protectivelayer and forming the electrically conductive polymer layer over theprotective layer to thereby coat the protective layer.
 3. A method offabricating microneedles according to claim 2 wherein, after forming theelectrically-conductive polymer layer which coats the protective layer,a combined thickness of the protective layer which coats the mold pillarand the electrically-conductive layer which coats the protective layeris relatively thick in regions closer to the substrate and relativelythin in regions more distal from the substrate.
 4. A method according toclaim 2 wherein, a thickness of the electrically-conductive layer whichcoats the protective layer is relatively thick in regions closer to thesubstrate and relatively thin in regions more distal from the substrate.5. A method according to claim 2 comprising: removing the firstmicroneedle from the mold pillar by separating at least the metal layerfrom the mold pillar and the protective layer; and forming a secondelectrically conductive layer over the protective layer to coat theprotective layer and to thereby provide a second microneedle.
 6. Amethod according to claim 5 wherein forming the second electricallyconductive layer over the protective layer to coat the protective layerand to thereby provide the second microneedle comprises: forming asecond electrically-conductive polymer layer which coats the protectivelayer; and depositing a second metal layer over the secondelectrically-conductive polymer layer to provide a second microneedle.7. A method according to claim 6 wherein, after forming the secondelectrically-conductive polymer layer which coats the protective layer,a thickness of the layers that coat the mold pillar is relatively thickin regions closer to the substrate and relatively thin in regions moredistal from the substrate, and wherein the second microneedle exhibits acorresponding shape.
 8. A method according to claim 5 wherein removingthe first microneedle from the mold pillar by separating at least themetal layer from the mold pillar and protective layer comprises at leastpartially dissolving the first electrically-conductive polymer layer, tothereby separate the metal layer from the protective layer.
 9. A methodaccording to claim 2 wherein forming an electrically-conductive polymerlayer which coats the protective layer comprises: applying a solution tocoat the protective layer, the solution comprising a polymer andconductive particles dissolved in a solvent; and evaporating the solventfrom the mold pillar to leave behind the electrically-conductive polymerlayer on the mold pillar.
 10. A method according to claim 9 whereindepositing the metal layer over the one or more coating layers toprovide the first microneedle comprises: electroplating the metal layeronto the electrically-conductive polymer layer; and using theelectrically-conductive polymer layer as an electrode in theelectroplating process.
 11. A method according to claim 2 whereindepositing the protective layer over the mold pillar to thereby coat themold pillar with the protective layer comprises: dissolving a polymerinto a solvent to provide a protective layer solution; applying theprotective layer solution to the mold pillar to coat the mold pillar;and curing the polymer to form the protective layer from the curedpolymer.
 12. A method according to claim 11 wherein applying theprotective layer solution to the mold pillar comprises at least one of:spin-casting the protective layer solution; and solvent-casting theprotective layer solution.
 13. A method according to claim 11 whereincuring the polymer to form the protective layer from the cured polymercomprises at least one of: applying electromagnetic radiation to thepolymer; and applying heat to the polymer.
 14. A method according toclaim 11 wherein depositing the protective layer over the mold pillar tothereby coat the mold pillar with the protective layer furthercomprises, prior to curing, evaporating the solvent from the protectivelayer solution to leave behind the polymer and to thereby coat the moldpillar with the polymer.
 15. A method according to claim 14 whereindepositing the protective layer over the mold pillar to thereby coat themold pillar with the protective layer comprises, after evaporating thesolvent from the protective layer, baking the combination of the moldpillar and the polymer using a plurality of discrete baking steps, eachsuccessive baking step in the series of baking steps involving a longertemporal duration and higher temperature.
 16. A method according toclaim 11 wherein depositing the protective layer over the mold pillar tothereby coat the mold pillar with the protective layer comprises, priorto curing the polymer to form the protective layer from the curedpolymer, baking the combination of the mold pillar and the polymer usinga plurality of discrete baking steps, each successive baking step in theseries of baking steps involving a different temporal duration anddifferent temperature.
 17. A method according to claim 1 whereinfabricating the mold pillar comprises applying a photoresist layer to asubstrate, exposing a portion of the photoresist layer to actinicradiation through a mask and, after exposing, dissolving at least someof the photoresist layer to remove the at least some of the photoresistlayer from the substrate to leave behind the mold pillar.
 18. A methodaccording to claim 17 wherein forming the one or more coating layers onthe mold pillar comprises depositing a protective layer over the moldpillar to thereby coat the mold pillar with the protective layer andforming the electrically conductive polymer layer over the protectivelayer to thereby coat the protective layer.
 19. A method according toclaim 18 comprising: removing the first microneedle from the mold pillarby separating at least the metal layer from the mold pillar andprotective layer; and forming a second electrically conductive layerover the protective layer to coat the protective layer and to therebyprovide a second microneedle.
 20. A method according to claim 19 whereinforming the second electrically conductive layer over the protectivelayer to coat the protective layer and to thereby provide the secondmicroneedle comprises: forming a second electrically-conductive polymerlayer which coats the protective layer; and depositing a second metallayer over the second electrically-conductive polymer layer to provide asecond microneedle.
 21. A method according to claim 20 wherein, afterforming the second electrically-conductive polymer layer which coats theprotective layer, a thickness of the layers that coat the mold pillar isrelatively thick in regions closer to the substrate and relatively thinin regions more distal from the substrate, and wherein the secondmicroneedle exhibits a corresponding shape.
 22. A method according toclaim 19 wherein removing the first microneedle from the mold pillar byseparating at least the metal layer from the mold pillar and theprotective layer comprises at least partially dissolving the firstelectrically-conductive polymer layer, to thereby separate the metallayer from the protective layer.
 23. A method according to claim 17comprising after exposing the portion of the photoresist layer toactinic radiation through the mask and prior to dissolving at least someof the photoresist layer, baking the combination of the substrate andthe photoresist layer using a plurality of discrete baking steps, eachsuccessive baking step in the series of baking steps involving a longertemporal duration and higher temperature.
 24. A method according toclaim 1 comprising: removing the first microneedle from the mold pillarby separating at least the metal layer from the mold pillar and at leastone of the one or more coating layers; forming a second electricallyconductive layer over the at least one of the one or more coating layersto thereby provide a second microneedle.
 25. A method according to claim24 wherein forming the second electrically conductive layer over the atleast one of the one or more coating layers to thereby provide thesecond microneedle comprises: forming a second electrically-conductivepolymer layer which coats the at least one of the one or more coatinglayers; and depositing a second metal layer over the secondelectrically-conductive polymer layer to provide a second microneedle.26. A method according to claim 25 wherein, after forming the secondelectrically-conductive polymer layer which coats the at least one ofthe one or more coating layers, a thickness of the layers that coat themold pillar is relatively thick in regions closer to the substrate andrelatively thin in regions more distal from the substrate, and whereinthe second microneedle exhibits a corresponding shape.
 27. A methodaccording to claim 24 wherein removing the first microneedle from themold pillar by separating at least the metal layer from the mold pillarand the at least one of the one or more coating layers comprises atleast partially dissolving the first electrically-conductive polymerlayer, to thereby separate the metal layer from the at least one of theone or more coating layers.
 28. A method according to claim 1 whereindepositing the metal layer over the one or more coating layers toprovide the first microneedle comprises: electroplating the metal layeronto the electrically-conductive polymer layer; and using theelectrically-conductive polymer layer as an electrode in theelectroplating process.
 29. A method according to claim 1 whereinforming one or more coating layers on the mold-pillar, the one or morecoating layers comprising an electrically-conductive polymer layercomprises: applying a solution to coat the mold pillar, the solutioncomprising a polymer and conductive particles dissolved in a solvent;and evaporating the solvent from the mold pillar to leave behind theelectrically-conductive polymer layer on the mold pillar.